The invention relates to an infinitely variable traction roller transmission in which power is transmitted through traction rollers pivotally supported in a housing between toric input and output discs.
In such transmissions, the traction rollers are mounted on support structures which, when pivoted, cause engagement of the traction rollers with the toric discs in circles of varying diameters depending on the desired transmission ratio. The pivotal traction roller support structures are so supported that they can be moved axially for initiating a change in the transmission ratio. For example, two traction rollers may be supported opposite one another by flexible tension sheets as shown in U.S. Pat. No. 4,086,820 which issued May 2, 1978 to Charles E. Kraus.
In the arrangement according to the present inventor's U.S. Pat. No. 4,702,118, the traction roller support members are pivotally supported with respect to the transmission housing by means of antifriction bearing segments which are disposed at opposite ends of the support members and directly mounted on the housing. Such bearing segments however are quite expensive and therefore the arrangement as a whole becomes too expensive for small transmissions.
In applicant's U.S. Pat. No. 4,858,484 in which two traction rollers are arranged between, and in engagement with, opposite toric traction discs for the transmission of motion therebetween, each traction roller is supported by a pivotal support trunnion which has support rollers disposed at opposite ends thereof and supported on partial circular tracks disposed on the housing's inner surface for direct trunnion support. The traction rollers are supported on the pivot trunnions by force transmitting means which, for inexpensive transmissions, include stacks of Belleville springs. The housing tracks may have a center of curvature which is slightly off-set with regard to the pivot axis of the trunnions in order to provide greater compression of the Belleville spring, that is, greater disc engagement forces in one pivotal end position of the pivot trunnions than in their opposite pivotal end positions.
Such support structure is relatively inexpensive and yet with the arrangement with displaced support track the engagement forces applied to the traction rollers by the traction roller support structure depend on the pivot position of the traction roller support trunnion such that--depending on the use of the transmission--they are relatively high in one pivot end position and relatively low in the opposite pivot end position. This arrangement, although relatively simple and inexpensive, still requires a high pressure fluid source and high pressure operating cylinders and pistons for transmission ratio control and although the high pressure control structures are relatively simple they were the cause of a number of operational difficulties and furthermore they require a special high pressure fluid pump since operating fluids of similarly high pressures are generally not available.
It is therefore the object of the present invention to provide a relatively simple infinitely variable traction roller transmission which can be operated without hydraulic operating means or with only low pressure hydraulic operating mechanisms.